In order to linearize radio transmissions, radio frequency transmitters and receivers use differential architectures. Antennas, as well as the power amplifiers associated with them, do not have this differential structure, however. A transformation of the differential signals from communication circuits should therefore be performed before they are delivered to the power amplification stage and the antenna (antenna stage, for short).
The radio transmitters and receivers of today operate in different modes and on different frequency bands. In addition, transmitters and receivers currently have different outputs for various applications. For example, some devices can operate in compliance with different standards, and therefore have different antenna stages (for example operating in WCDMA and in GSM/EDGE).
Magnetic transformers are used to perform this transformation and also to match the output from these circuits to a particular antenna amplifier.
These transformers comprise inductors, and including these inductors in an integrated circuit requires a large silicon surface area.
A large amount of space is therefore consumed in the integrated circuit, as each antenna stage requires a circuit that has a transformer.
A prior art radio frequency circuit will now be described with reference to FIG. 1.
A matching circuit MATCH is positioned between two communication circuits CIRC1 and CIRC2 on the one hand and two antenna amplifiers AMPLI1 and AMPLI2 on the other hand. The antenna amplifiers APMLI1 and APMLI2 are respectively connected to the antennas ANT1, ANT2.
The circuit MATCH comprises two transformers TRSFO1 and TRSFO2, respectively coupled to the circuits CIRC1 and CIRC2.
The circuits CIRC1 and CIRC2 have a differential structure. The two outputs from each circuit are connected to the two terminals of the transformers' primary circuits. The transformers' secondary circuits have a terminal connected to the ground and a terminal connected to each of the amplifiers AMPLI1 and AMPLI2.
Two separate transformers are therefore used in this structure. Each of these transformers occupies space on the silicon substrate.